In a semiconductor integrated circuit device, silicon, for example, an amorphous silicon is used in filling a contact hole or line, or as a thin film material for forming a device or structure. There is known a technique for forming an amorphous silicon film by decomposing disilane at a temperature ranging from 400 to 500 degrees C., trisilane at a temperature ranging from 350 to 450 degrees C., or tetrasilane at a temperature ranging from 300 to 400 degrees C.
However, when a miniaturized contact hole or line is filled with the amorphous silicon, a film formed by the amorphous silicon has poor coverage in the contact hole (or line), which results in large voids. These large voids may cause, e.g., an increase in resistance. Also, this may cause degradation in accuracy of surface roughness of the amorphous silicon film.
In order to avoid a degradation of the accuracy of the surface roughness of the amorphous silicon film, there is also known an approach for supplying, before the formation of the amorphous silicon film, an aminosilane-based gas onto a surface of an underlayer such that a seed layer is formed on the surface.
In recent years, in addition to improving the accuracy of the surface roughness of the silicon film (e.g., the amorphous silicon film), further reduction in temperature of a film forming process is desired.
The aforementioned approach is capable of achieving an improvement to the accuracy of the surface roughness, but is mainly applied to a case where a temperature of the film forming process is equal to or more than 400 degrees C. For example, if the approach is applied to a film forming process having a temperature of less than 400 degrees C. (e.g., 350 degrees C.) as an upper limit, an incubation time of the amorphous silicon film that is formed on the seed layer is slightly increased.
This may result in a slight deterioration in the accuracy of the surface roughness. Such deterioration, although is not problematic as it now stands, may be elevated to an unacceptable level as the development of an electron device advances.
Accordingly, taking into account the further reduction in temperature of the film forming process, it is difficult to maintain or improve the accuracy of the surface roughness of the thin film formed on a seed layer, and to achieve further improvement of in-plane uniformity.